Patent GB-1508750-A (GB)
Title: Transmit-receive circuit changing switch system
IPC: H04B1/46
Filed: 1976-04-30
Abstract: 1508750 Transmit-receive switching; pulse handling TANI DENKI KOGYO KK 30 April 1976 [28 May 1975 19 June 1975 24 June 1975] 17795/76 Headings H4L and H3T In radio-telephone equipment a switching signal generator 9, Fig. 10; or Figs. 8, 13 (not shown) controls antenna switch 2 to establish the transmit mode 2a-2c when an audio signal taking the form of a pulse signal produced by a particular vocalization by an operator and originating from transducer {mike/speaker} 5 having the form of an earplug type transducer inserted into the operator's ear is detected, there being provision to ensure that audio signals originating from the receiver 3 when in the receive mode do not actuate the generator 9, the generator providing a rectangular waveform to control switch 2. In the transmit mode, the rectangular waveform from generator 9 additionally enables the transmitter and disenables the receiver, and provides a signal disenabling the transmitter and enabling the receiver otherwise. The provision comprises either the combination of a low pass filter (12), Fig. 4 (not shown) at the input of the generator (9), and a high pass filter (11) at the receiver output, the series combination of the two Fig. 5 (not shown) between the receiver and generator providing the necessary attenuation, the transmitter (7, Fig. 4) being directly coupled between the transducer (5) and switch 2; or a transmit/receive switch 4 normally connecting the transducer 5 to the transmitter 7, but changed over by control 6 to the receiver when r.f. is received, antenna switch 2 normally being in the receive position 2a-2b, Fig. 1 showing the disposition of switches 2, 4 for standby. The filters (11, 12, Fig. 4) may be supplemented by a hybrid circuit (13), Fig. 6 (not shown) providing low attenuation to the transducer (5) and high attenuation in the interfilter path (11-12), or by a matching impedance (14), Fig. 7 (not shown). Upon receipt of the particular vocalization signal, in the form of a pulse, or a pair of pulses, the transmit mode is selected for a predetermined time, whence reversion to receive mode takes place. Should, during this time, a further pulse or spaced pair thereof be produced, reversion to receive mode takes place. A pulse, or pair of pulses produced after the receive mode is regained, causes reversion to transmit mode for a further predetermined time. Switching signal generator (Fig. 10).-Monostables 94, 96 are normally in the reset state {receive}. A voice pulse at 90 sets monostable 94 for a time (t, Fig. 11) determined by the time constant R 1  C 1 , and, after a delay d 1 <t 1  provided by delay 95, gate 92 is enabled, gate 91 being disenabled so that if the pulse still exists at this time, see Fig. 12 (not shown), or a second pulse is produced after d, and before t 1 , monostable 96 is set to provide the "transmit" control signal at 99, the signal enduring for a time t 2  determined by the time constant R 3 C 3 . After a delay d 2  determined by R 4 C 4 , gate 93 is enabled, so that any input voice pulse after this time resets the monostable, reestablishing the "receive" mode. Otherwise the receive mode is re-established after time t 2 . A modified gate arrangement (91-93, 98) Fig. 13 (not shown) may be provided so that, a long pulse, or spaced pair of pulses are needed to re-establish the receive mode. A simplified circuit, Fig. 8 (not shown), comprising a single monostable and delay, and responsive to single pulses, may be provided.